The present invention generally relates to a method for continuously electrolyzing an elongated product such as strip, wire, foil, or the like of aluminum or an aluminum alloy, and to an apparatus for use for practicing such an electrolytic treatment. More particularly, the invention relates to an electrolytic treatment apparatus and a method for electrolytic treatment which overcomes various problems which occur in the high-speed running of a production line or in the electrolytic treatment of a thickly coated product.
Conventionally, continuous electrolytic treatment of an elongated product of aluminum or-an aluminum alloy (hereinafter simply referred to as an aluminum product) has been used widely, not only as an anodizing treatment for use in producing planographic supports, aluminized wires, electrolytic capacitors, etc., but also in an electrolytic coloring treatment, electrolytic polishing treatment, electrolytic etching treatment, and the like.
More particularly, a conventional electrolytic treatment apparatus as shown in FIG. 3 has been commonly used for continuous electrolytic treatment for an aluminum product. An electrolytic treatment method using such an apparatus is known, for example, as disclosed in Japanese Patent Unexamined Publications Nos. Sho-48-26638 and Sho-47-18739, and Japanese Patent Publication No. Sho-58-24517. Such a method involves an electrolytic treatment in which electric power is fed by a so-called submerged power supply system. For example, in a DC anodizing method using a conventional apparatus, an aluminum product 1, which is an object to be treated, runs from the left to the right in FIG. 3. An electrolytic treatment cell is constituted by three cells, that is, a power supply section 2 for negatively charging the aluminum product 1, an electrolytic 10 section 4 for electrolyzing the negatively charged aluminum product 1, and an intermediate section 3 provided for preventing a current from flowing between the respective cells of the power supply section 2 and the electrolytic section 4. In this case, currents from DC power sources 7a and 7b flow from a power supply electrode 5 into the aluminum product 1 through the electrolyte in the power supply section 2. Further, the currents flow into the aluminum product 1 toward the electrolytic section 4, and flow from the aluminum product 1 into electrolytic electrodes 6 a and 6b through the electrolyte in the electrolytic section 4. In the electrolytic section 4, an anodic oxidation coating film is generated on the surface of the aluminum product 1.
According to the submerged power supply method, it is possible to prevent generation of sparks in power feeding and the generation of scar faults and the like because the object to be treated is not brought into contact with electrodes or the like, unlike the conventional direct power supply method. It is therefore possible to realize a highly stable electrolytic treatment line. In this method, however, it is necessary to increase the magnitude of the current supplied when the speed of the electrolytic treatment line is increased for the purpose of improving productivity or when the quantity of anodic oxidation coating film must be increased for the purpose of improving the product quality. When the magnitude o of the supplied current is raised, the voltage drop due to ohmic loss in the aluminum product 1 increases, and it is therefore necessary to employ power supplies capable of providing a high electrolytic voltage.
As a result of such an increase of the current and voltage of the power supply, the cost of the requisite electric power is increased, thereby increasing production costs. Also, the larger power source increases the equipment cost. Moreover, increasing the electrolytic voltage increases the amount of Joule heating generated in the aluminum product 1 in the o portion between the power supply electrode 5 and each of the electrolytic electrodes, resulting in an increase in costs associated with cooling the aluminum product 1 and the electrolytes to a regulated temperature.
In the intermediate section 3 between the power supply section 2 and the electrolytic section 4, all the currents to be supplied to the aluminum product 1 flow in such a manner that, in the case of a product having a small cross-sectional area such as a wire, foil, thin strip, or the like, heat is excessively generated, thereby resulting in fusing of the aluminum product 1. Consequently, there is a limit to increasing the feeding current, and it has been therefore difficult to increase the speed of treatment using the conventional method.
Further, for example, in the case where there is employed a post-treatment step following the electrolytic treatment involving, for example, application of an organic solvent, it has generally been necessary to ground the aluminum product following the electrolytic treatment step using, for example, a grounding roll 8 as shown in FIG. 4. The reason for this is to prevent explosion, ignition, or the like due to an increase of the electric potential of the aluminum product in the post-treatment steps.
In this method, however, the electric potential of a portion of the aluminum product at the front side of the electrolytic treatment section is higher than ground potential, although the electric potential of a portion of the aluminum product at the rear side of the electrolytic treatment section is substantially equal to ground potential. A current is therefore generated which flows from the electrolytic treatment section to the forward portion along a line through the aluminum product. Due to this current, various problems such as corrosion of metal parts used in supporting pipes or a liquid carrier pump, sparking, leakage of electricity, or the like occur in various devices for used in treatments preceding the electrolytic treatment.
Further, there has been a problem in that, in order to prevent the foregoing problems, it is necessary to use a noncorrosive material or an insulating material in constructing the equipment, which makes the equipment complicated, increasing the equipment cost as well as the maintenance cost.
Moreover, if the speed of the electrolytic treatment line is increased for the purpose of improving productivity or when the thickness of an anodic oxidation coating film is increased for the purpose of improving product quality, it is particularly necessary to increase the magnitude of the feeding current, and therefore the electrical potential of the aluminum product at a portion thereof at the front side of the electrolytic treatment section becomes higher, which exacerbates the foregoing problems.